Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D15/00—Control, e.g. regulation, of pumps, pumping installations or systems
  • F04D15/0088—Testing machines
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D29/00—Details, component parts, or accessories
  • F04D29/08—Sealings
  • F04D29/10—Shaft sealings
  • F04D29/106—Shaft sealings especially adapted for liquid pumps
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D29/00—Details, component parts, or accessories
  • F04D29/08—Sealings
  • F04D29/16—Sealings between pressure and suction sides
  • F04D29/165—Sealings between pressure and suction sides especially adapted for liquid pumps
  • F04D29/167—Sealings between pressure and suction sides especially adapted for liquid pumps of a centrifugal flow wheel
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16J—PISTONS; CYLINDERS; SEALINGS
  • F16J15/00—Sealings
  • F16J15/16—Sealings between relatively-moving surfaces
  • F16J15/32—Sealings between relatively-moving surfaces with elastic sealings, e.g. O-rings
  • F16J15/3284—Sealings between relatively-moving surfaces with elastic sealings, e.g. O-rings characterised by their structure; Selection of materials
  • F16J15/3292—Lamellar structures
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D1/00—Radial-flow pumps, e.g. centrifugal pumps; Helico-centrifugal pumps
  • F04D1/06—Multi-stage pumps
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
  • F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
  • F05D2240/00—Components
  • F05D2240/55—Seals
  • F05D2240/59—Lamellar seals

Definitions

• the present disclosure concerns improvements to centrifugal pumps, in particular but not exclusively multi-stage centrifugal pumps. More specifically, the present disclosure relates to improvements aimed at increasing the efficiency of centrifugal pumps having a low specific speed.
• Multi-stage centrifugal pumps are widely used to boost the pressure o liquids.
• a multi-stage centrifugal pump usually comprises a casing and a shaft arranged for rotation in the casing.
• a plurality of impellers is keyed on the shaft and are rotatingly housed in respective chambers formed in the pump casing.
• Inter-stage sealing rings and bushings are fit in the casing and co-act with the respective impellers to seal each side of each impeller, thus preventing the pressurized liquid delivered at the outlet of one impeller to flow back towards the upstream stage.
• the efficiency of the sealing rings and sealing bushings heavily influence the overall efficiency of the pump.
• Brush seals have been suggested in centri ugal pumps in applications where the processed fluid contains solid particles or is a multi-phase fluid. Brush seals, however, have a limited sealing efficiency and have a limited pressure drop capability.
• the disclosure concerns an improved sealing arrangement capable of increasing efficiency of a single-stage or multi-stage centrifugal pump comprising a casing, a rotary shaft arranged for rotation in said casing and a one or a plurality of pump stages.
• Each pump stage comprises an impeller secured on the rotary shaft and arranged for rotation in a respective impeller chamber.
• a plurality of sealing members are further provided, for reducing leakage between a rotary component and a respective stationary component of the pump.
• at least one of the sealing members in at least one of the pump stages comprises an arrangement of compliant plates or compliant plate members attached in facing relation at root ends to the respective stationary component and forming a sealing ring between the stationary component and the respective rotary component.
• One or more of the pump stages have a specific speed defined as
• each pump stage has a low specific speed, not higher than 25.
• the pump can be comprised of N stages and N-l stages have a specific speed equal to or less than 25.
• the first stage i.e. the one nearer to the pump inlet or suction side can be different from the remaining stages and have a specific speed higher than 25.
• each stage of the pump comprises an inlet-side sealing member and an outlet-side sealing member.
• At least the inlet-side sealing member of at least one, some or all the stages are comprised of compliant plate members arranged in facing relation as described above.
• at least the inlet sealing member is comprised of compliant plate members.
• the inlet-side sealing member can be arranged for co-action with an impeller eye of the respective impeller.
• the outlet-side sealing member can be arranged for co-action with an impeller hub of the respective impeller.
• one, some or all the outlet-side sealing members of the pump stages are comprised of compliant plate members.
• sealing members comprising compliant plate members are used, between a stationary part or component of the casing and a portion of the rotary shaft or a portion of a component, such as a bushing or the like integrally rotating with the rotary shaft.
• Additional sealing members formed by compliant plate members can be provided between an outermost pump stage and a shall end containing the mechanical seals that isolates the pump from atmosphere.
• the pump can be provided with a balancing drum.
• One or more sealing members co-acting with the balancing drum can be provided.
• One or more said sealing members can be comprised of or formed by compliant plate members.
• the compliant plate members advantageously have a flat configuration, with a cross section having a first dimension in axial direction and a second dimension in tangential direction (thickness of the plate), the first dimension being larger than the second dimension, i.e. the compliant plates have a width in the axial direction much larger than the thickness thereof.
• the axial dimension is at least 10 times the tangential dimension.
• the narrow cross section of the compliant plate provides flexural deformability in the tangential direction and stiffness in the axial direction.
• Compliant plates-sealing arrangements are known per se. Their application in turbines is known. However, compliant plate members have not been envisaged for turbo-pumps.
• Compliant plate sealing members are characterized by a total leakage flow, which is the combination of the leakage between the tip ends of the compliant plate members and the rotary component and of the leakage between adjacent compliant plate members. The first contribution is proportional to the sealing diameter and the second contribution is proportional to the seal height and shaft diameter. In turbo-pump sealing arrangements the ratio between the seal height and the scaling diameter is 4-5 times greater than in turbines. Compliant plate sealing arrangements in pumps would therefore result in unacceptable leakage flows.
• a labyrinth seal comprising compliant plate members with one or more slits extending from the radially outmost root end towards an intermediate location along the plate height.
• One or more stationary rings, constrained to the stationary part of the sealing arrangement extend radially inwardly in the slits of the compliant plate members forming a labyrinth, which increases efficiency of the sealing arrangement.
• Fig. I illustrates a schematic section of a multi-stage, low specific speed pump
• Fig.2 illustrates an enlargement of one stage of the pump of Fig.1 ;
• Fig.3 illustrates a sectional view of one compliant plate seal
• Fig.4 illustrates a schematic view of a compliant plate sealing arrangement.
• Fig.1 illustrates a longitudinal section according to a vertical plane of a multi-stage centrifugal pump 1.
• the centrifugal pump 1 has a casing indicated generally at 3 and comprised of a barrel 5 and a cover 7.
• the casing 3 houses a driven shaft 9 supported by end bearings 11 , 13.
• a plurality of impellers 15 are torsionally connected on shaft 9 and rotate therewith.
• Each impeller 15 can be housed in a chamber 17 having an axial inlet 19 and a radial outlet 21 (see in particular Fig.2).
• the chambers 17 are connected in series.
• Each impeller 15 and respective chamber 17 form one pump stage.
• the centrifugal pump 1 is a so-called back-to-back pump, with a suction manifold 23 A and a delivery or discharge manifold 23 B.
• the impellers 15 are divided in two wells of oppositely arranged impellers, labeled 15X and 15 Y respectively, arranged in a back-to-back configuration.
• the inlet flow through suction manifold 23A is processed sequentially in a first, inlet impeller 16, in the first series of impellers 15X, subsequently in the second series of impellers 15Y and is finally delivered through the discharge manifold 23B.
• Fluid channeling connecting the two sets of impellers is provided between the outer barrel 5 and an inner casing portion 4, wherein the chambers 17 are formed.
• the inner casing portion 4 can be formed by two halves connected to one another along a plane parallel to the section of Fig.1 .
• each impeller 15 comprises an impeller hub 15H and an impeller shroud 15S, between which a plurality of blades 15B are arranged.
• an inlet side sealing member and an outlet side sealing member can be provided.
• an inter-stage sealing ring 27 is arranged at the inlet side of the stage and forms an inlet-side sealing member of the pump stage.
• the inter-stage sealing ring 27 is arranged between a stationary portion of the pump casing and an impeller eye 15E formed by the impeller shroud 15S and co-acts with said impeller eye 15E.
• an inter-stage sealing bushing 29 is arranged at the outlet side of the stage, between the casing 3 and the hub 15H of the impeller 1 5.
• the sealing bushing 29 forms an outlet-side sealing member of the pump stage.
• the sealing rings and sealing bushings here also cumulatively designated ''sealing members", prevent pressurized liquid exiting the impeller from returning towards the inlet of the stage, as well as liquid at the inlet of the subsequent stage to enter the previous stage from the back of the impeller 15.
• further sealing arrangements are provided in various axial positions along the shall 9 of the centrifugal pump 1.
• radial shaft-sealing members are shown at 31 and 35, near the bearings 1 1 , 13 of the shaft 9.
• a further intermediate radial shaft-sealing member 33 can be arranged in an intermediate position of the shaft 9, between the shaft and the stationary casing 3, separating the two sets of back-to-back arranged impellers 15X and 15Y.
• the shaft-sealing member 31 is arranged between a shaft terminal portion A and the outermost impeller of impeller group 15X.
• the shaft-sealing member 35 is arranged between the opposite shaft terminal portion 9B and the outermost impeller of the impeller group 15Y.
• An auxiliary pump stage with a dual impeller 16 can be provided between the shaft-sealing member 35 and the shaft terminal portion 9B.
• the shaft terminal portions 9 A, 9B are supported in the end bearings 1 1 , 13, respectively.
• Outer mechanical sealing members 12 and 14 can further be provided between each bearing 1 1 , 13 and the shaft-sealing members 31 and 33, respectively.
• At least one of the sealing members 27, 29, 31 , 33, 35 is designed as a compliant plate sealing arrangement.
• only one, some or all the shaft-sealing members 31 , 33, 35, arranged on the rotary shaft 9 are designed as compliant plate sealing arrangements.
• only the inlet side sealing members 27, or the outlet side sealing members 29 or both, are designed as compliant plate sealing members.
• all the sealing members 27, 3 1 , 33 and 35 and possibly also the sealing members 29 are designed as compliant plate sealing members.
• Figs 3 and 4 illustrate a longitudinal section along a plane containing the rotation axis of the centrifugal pump 1 and a perspective view of an exemplary arrangement of compliant plate members forming a sealing member.
• Figs. 3 and 4 illustrate one of the sealing rings 27 provided around the impeller eye of the impellers 15.
• the sealing member 27 comprises a housing 37, which is stationarily connected to the pump casing 3.
• the housing 37 can be comprised of a back ring 39 and a front ring 41.
• the back ring 39 and/or the front ring 41 can be omitted.
• the front ring 41 and the back ring 39 are formed as an integral part of the housing 37.
• the front ring can be machined in the casing 3.
• an intermediate annular wall 42 is provided between the back ring and the front ring.
• the housing 37 forms a stationary component of the sealing arrangement.
• each compliant plate member 43 has a root end or root 43 R and a tip end or tip 43T, the root end 43 R being the radially outmost edge of the compliant plate member and the tip being the radially innermost edge of the compliant plate member.
• the compliant plate members 43 are secured at their root ends 43 to the housing 37.
• the root ends of the compliant plate members 43 are secured to the intermediate annular wall 42.
• the compliant plate members 43 extend radially inwardly towards the rotation axis A- A of the shaft 9 and their tip ends 43T are arranged near or in contact with the respective rotary component, in the example illustrated in Figs 3 and 4 the impeller eye 15E of the respective impeller 15.
• the compliant plate members 43 are arranged in faced relationship, i.e. face-to- face, and inclined with respect to the radial direction, to allow rotation of the shaft 9 in the rotary direction fR (Fig.4).
• each compliant plate member has a generally laminar shape.
• Each compliant plate member can have a substantially rectangular cross section, with a dimension in the axial direction, which is much larger than the dimension in the tangential direction.
• the compliant plate members are therefore axially stiff, but have a bending flexibility in the tangential direction.
• each compliant plate member 43 comprises at least one slit extending from the root end 43 R of the compliant plate member 43 to an intermediate position along the radial extension of the compliant plate member.
• each compliant plate member 43 comprises three slits 45 A, 45 B, 45C.
• the slits are preferably rectilinear and extend in a radial direction.
• the central slit 45 B is longer than the side slits 45A, 45C.
• the compliant plate members 43 are arranged such that the slits 45 A, 45 B, 45 C are aligned. This arrangement forms three annular slots extending around the sealing arrangement formed by the compliant plate members 43.
• Corresponding rings 47 A, 47B, 47C secured to the housing 37 extend radially into the respective slots formed by the aligned slits 45A, 45 B, 45C of the compliant plate members.
• the rings 47A, 47B and 47C extend from the intermediate annular wall 42 of the housing 37.
• the rings 47 A, 47B and 47C as well as the annular slots formed by the slits 45A, 45B, 45C in the facing compliant plate members 43 can have variable radial lengths. They can also have a variable axial width. While in the embodiment illustrated in Figs 3 and 4 three slits 45A, 45 B, 45C are provided in each compliant plate member 43, a different number of slits and correspondingly a different number of rings 47 A, 47B, 47C can be provided, based e.g. on design considerations. In other, less advantageous embodiments, no rings and no slots are provided.
• the compliant plate members will in that case be solid rather than slotted as depicted in the figures.
• the shape of the slits and the cross sectional shape of the rings can be rectangular, as shown in the exemplary embodiment, but other shapes can be used instead.
• the slits and the annular rings can have a V-shaped or a U-shaped cross section.
• the outer perimeter of the compliant plate members 43 can be rectangular, as illustrated, or differently shaped, e.g. T-shaped, trapezoidal or the like, e.g. with increasing width from the root end to the tip, or vice-versa.
• each compliant plate member 43 provides axial stiffness and bending flexibility in the tangential direction, as noted above.
• the sealing member formed by the annul arly arranged compliant plate members 43 provides an efficient sealing functionality also in case of large pressure differences between the back and front sides of the sealing member, i.e. in case of large head values, thanks to the axial sti fness provided by the substantially planar shape of the compliant plate members 43. Thanks to the stiffness of the compliant plate members 43 in the axial direction, even in case of high differential head across the pump stage, the deformation of the sealing arrangement in the axial direction will be negligible, thereby preserving the sealing functionality.
• the combination of the one or more radial rings 47 A, 47B, 47C and circumferential slots formed by the slits 45 A, 45B, 45C of the compliant plate members 43 provide a labyrinth sealing effect, imposing a tortuous path to the leakage flow from the pressure side to the suction side of the sealing member, thereby increasing the resistance to leakage flow.
• This particularly efficient sealing arrangement results in an increased efficiency of centrifugal pumps characterized by a low specific speed.
• the specific speed of a stage of a centrifugal pump can be defined as
• q flow rate (m 3 /h, 1/s, 1/min, m 3 /min, US gpm, British gpm) at Best Efficiency Point
• a low specific speed centrifugal pump stage is one where the specific speed is
• Ns ⁇ 25 (in the SI system) Ns ⁇ 1290 in the US system.
• a multistage centrifugal pump usually has a plurality of stages with identical impellers.
• the multistage pump having a low specific speed is one where all the stages have a low specific speed.
• the first stage of the multistage centrifugal pump has an impeller, which differs from the remaining impellers o the centrifugal pump and which can have a higher specific speed.
• compliant plate members in centrifugal pumps, especially multi-stage centrifugal pumps, allows reducing the number of stages and therefore the number of impellers, increasing the head, i.e. the pressure difference, across each stage, maintaining a high overall pump efficiency, due to the sealing functionality of the compliant plate sealing members.

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• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Structures Of Non-Positive Displacement Pumps (AREA)
• Sealing Using Fluids, Sealing Without Contact, And Removal Of Oil (AREA)

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Citations (5)

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• 2012
  • 2012-10-15 IT IT000210A patent/ITFI20120210A1/it unknown
• 2013
  • 2013-10-14 BR BR112015007115A patent/BR112015007115B8/pt active IP Right Grant
  • 2013-10-14 JP JP2015536172A patent/JP6442407B2/ja active Active
  • 2013-10-14 CA CA 2886985 patent/CA2886985A1/en not_active Abandoned
  • 2013-10-14 CN CN201380053915.2A patent/CN104813033B/zh active Active
  • 2013-10-14 US US14/435,507 patent/US20150260190A1/en not_active Abandoned
  • 2013-10-14 ES ES13774691T patent/ES2916804T3/es active Active
  • 2013-10-14 WO PCT/EP2013/071404 patent/WO2014060343A1/en active Application Filing
  • 2013-10-14 AU AU2013331741A patent/AU2013331741B2/en active Active
  • 2013-10-14 KR KR1020157012529A patent/KR102200789B1/ko active IP Right Grant
  • 2013-10-14 EP EP13774691.3A patent/EP2912318B1/en active Active

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